The animal cell Golgi apparatus is a complex interconnected reticulum composed of tubules and stacks of cisternae which receive the output of the endoplasmic reticulum. Proteins leave the endoplasmic reticulum and are transported through the Golgi stack. As they do so they are modified, sorted, and ultimately destined for specific membrane bound organelles. Mechanisms of protein and membrane traffic are rather controversial. In spite of the recent consensus assuming that proteins are carried out by vesicles a number of observations indicates that membrane tubules participate in the transportation as well. One of the most contradictory problem is the three-dimensional organization of the Golgi apparatus as a whole. The overall three-dimensional appearance of the Golgi complex is therefore ribbon-like, with alternating compact (stacked cisternae) and non-compact (tubular-reticular) zones; only the cis and trans poles of the complex are made mostly of convoluted tubules. In early spermatids, the saccules together with the membranous tubules seen in the intersaccular or peripheral Golgi regions, form a single continuous membranous system. Observation of the fractured Golgi apparatus confirm that almost each two adjacent stacks indeed continuous with each other. The connectivity between individual stacks is also evident in living cells. Laser bleaching of part of a Golgi complex containing chimeras between resident Golgi proteins and green fluorescent protein quickly induces the elimination of the fluorescence from other parts of the Golgi complex, suggesting rapid diffusional exchange of the Golgi enzymes between stacks. Although tubules are a prominent feature of the Golgi complex (Lindsey and Ellisman, 1985), in the norm they are almost never seen to link cisternae within the same stack, although in early spermatids tubules may occasionally cobridge saccules of the same stack. In this project we are collaborating with researchers at the National Center for Microscopy and Imaging Research to determine if tubules participate in the intracellular traffic. Serial section reconstructions of fast frozen cells have been performed. The structure of the Golgi apparatus stained with mannosidase II was also examined using IVEM. A manuscript detailing this work is in preparation.